U.S. patent application number 11/664666 was filed with the patent office on 2009-05-14 for time difference measuring device, measuring method, distance measuring device, and distance measuring method.
This patent application is currently assigned to KABUSHIKI KAISHA TOPCON. Invention is credited to Masahiro Ohishi, Fumio Ohtomo.
Application Number | 20090122296 11/664666 |
Document ID | / |
Family ID | 36142633 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090122296 |
Kind Code |
A1 |
Ohishi; Masahiro ; et
al. |
May 14, 2009 |
Time Difference Measuring Device, Measuring Method, Distance
Measuring Device, and Distance Measuring Method
Abstract
A time difference measuring device can accurately measure a time
difference between two pulse signals generated with a predetermined
time difference by measuring the two pulse signals by one
measurement. The time difference measuring device measures a time
difference between a start signal (M1) and a stop signal (M2). The
device has a reference signal generation unit (41) for generating
two reference signals (S1, S2) having a .pi./2 phase difference.
According to corresponding amplitude values (A11, A12) and (A21,
A22) of the reference signals (S1, S2) at each generation timing of
the start signal (M1) and the stop signal (M2), a phase difference
detection unit (42) calculates a phase difference .DELTA..theta.
(=.theta.stop-.theta.start) between the generation timings of the
pulse signals (M1, M2). According to the detected phase difference
.DELTA..theta. and the cycle (Ts) of the reference signals (S1;
S2), a time difference calculation unit (44) calculates the
generation time difference .DELTA.t between the pulse signals (m1,
M2).
Inventors: |
Ohishi; Masahiro; (Tokyo,
JP) ; Ohtomo; Fumio; (Tokyo, JP) |
Correspondence
Address: |
CHAPMAN AND CUTLER
111 WEST MONROE STREET
CHICAGO
IL
60603
US
|
Assignee: |
KABUSHIKI KAISHA TOPCON
Tokyo
JP
|
Family ID: |
36142633 |
Appl. No.: |
11/664666 |
Filed: |
September 30, 2005 |
PCT Filed: |
September 30, 2005 |
PCT NO: |
PCT/JP05/18142 |
371 Date: |
April 4, 2007 |
Current U.S.
Class: |
356/5.05 ;
702/176 |
Current CPC
Class: |
G04F 10/06 20130101;
G01S 7/497 20130101; G01S 17/14 20200101 |
Class at
Publication: |
356/5.05 ;
702/176 |
International
Class: |
G01C 3/08 20060101
G01C003/08; G04F 10/00 20060101 G04F010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 4, 2004 |
JP |
2004-291495 |
Jun 9, 2005 |
JP |
2005-169500 |
Claims
1. A time difference measuring device which measures a time
difference of two or more pulse signals generated with a
predetermined time difference, the time difference measuring device
comprising: a reference signal generation unit configured to
generate one or more reference signals; an amplitude detection unit
configured to obtain two amplitudes based on the one or more
reference signals so as to be substantially equal to sampling the
one or more reference signals, at predetermined two timings which
depend on generation timings of each of the pulse signals; a phase
difference detection unit configured to calculate a phase
difference between the generation timings of the pulse signals on
the basis of each of the amplitudes of the reference signals
obtained for each of the pulse signals, detected by the amplitude
detection unit; and a time difference calculation unit configured
to calculate a generation time difference of the two or more pulse
signals on the basis of the phase difference detected by the phase
difference detection unit and a cycle of the one or more reference
signals.
2. A time difference measuring device which measures a time
difference of two pulse signals generated with a predetermined time
difference, the time difference measuring device comprising: a
reference signal generation unit configured to generate at least
two reference signals having a phase difference of virtually
.pi./2; a phase difference detection unit configured to calculate a
phase difference of generation timings of the two pulse signals, on
the basis of amplitudes of the at least two reference signals at
each of the generation timings of the two pulse signals; and a time
difference calculation unit configured to calculate a generation
time difference of the two pulse signals, on the basis of the phase
difference detected by the phase difference detection unit and a
cycle of the at least two reference signals.
3. A time difference measuring device according to claim 1, further
comprising a coarse time difference detection unit configured to
detect a coarse generation time difference of the two or more pulse
signals, wherein the time difference calculation unit is configured
to calculate, in addition to a precise time difference calculated
on the basis of the phase difference detected by the phase
difference detection unit and the cycle of the one or more
reference signals, the generation time difference of the two or
more pulse signals by the coarse generation time difference
detected by the coarse time difference detection unit.
4. A time difference measuring device according to claim 1, wherein
the one or more reference signals includes at least one of a sine
wave signal and a cosine wave signal.
5. A time difference measuring device according to claim 4, wherein
the phase difference detection unit is configured to: detect an
amplitude A11 of the sine wave signal and an amplitude A12 of the
cosine wave signal, at the generation timing of one pulse signal
preceding in time series of the two or more pulse signals;
calculate a ratio A11/A12 of the amplitudes A11, A12; calculate a
phase .theta.start on the basis of the amplitude ratio A11/A12 by
tan.sup.-1(A11/A12); detect an amplitude A21 of the sine wave
signal and an amplitude A22 of the cosine wave signal, at the
generation timing of the other pulse signal succeeding in time
series of the two or more pulse signals; calculate a ratio A21/A22
of the amplitudes A21, A22; calculate a phase .theta.stop on the
basis of the amplitude ratio A21/A22 by tan.sup.-1(A21/A22); and
calculate a phase difference .DELTA..theta. of the generation
timings of the two or more pulse signals by
(.theta.stop-.theta.start).
6. A time difference measuring device according to claim 1, wherein
the reference signal generation unit is configured to originally
generate one reference signal, generate a new reference signal of
which phase is delayed by virtually .pi./2[rad] to the reference
signal originally generated, and generate the originally generated
reference signal and the new reference signal as the two reference
signals having the phase difference of virtually .pi./2.
7. A time difference measuring method which measures a time
difference of two pulse signals generated with a predetermined time
difference, the method comprising: detecting a coarse generation
time difference of the two pulse signals; generating a sine wave
signal and a cosine wave signal having the phase difference of
virtually .pi./2 as two reference signals; obtaining, on the basis
of the amplitudes of the sine wave signal and the cosine wave
signal at each of generation timings of the two pulse signals, a
phase difference of the generation timings of the two pulse
signals; and calculating a generation time difference of the two
pulse signals, on the basis of the obtained phase difference and a
cycle of the reference signals and the coarse generation time
difference.
8. A time difference measuring method according to claim 7,
comprising: detecting an amplitude A11 of the sine wave signal and
an amplitude A12 of the cosine wave signal, at the generation
timing of one pulse signal preceding in time series of the two
pulse signals, calculating a ratio A11/A12 of the amplitudes A11,
A12, calculating a phase .theta.start on the basis of the amplitude
ratio A11/A12 by tan.sup.-1(A11/A12), detecting an amplitude A21 of
the sine wave signal and an amplitude A22 of the cosine wave
signal, at the generation timing of the other pulse signal
succeeding in time series of the two pulse signals, calculating a
ratio A21/A22 of the amplitudes A21, A22, calculating a phase
.theta.stop on the basis of the amplitude ratio A21/A22 by
tan.sup.-1(A21/A22), and calculating a phase difference
.DELTA..theta. of the generation timings of the two pulse signals
by (.theta.stop-.theta.start).
9. A distance measuring device, comprising: a measuring wave
emission unit configured to emit a measuring wave to an object to
be distance-measured; a reflected wave detection unit configured to
detect a reflected wave acquired by the measuring wave reflected by
the distance measuring object; and a distance measuring unit
configured to acquire a first pulse signal at a timing of the
measuring wave emitted from the measuring wave emission unit,
acquire a second pulse signal at a timing of the reflected wave
detected by the reflected wave detection unit, and obtain a
distance to the distance measuring object on the basis of a time
difference from the timing of the first pulse signal acquired to
the timing of the second pulse signal acquired, wherein the
distance measuring unit includes the time difference measuring
device according to any one of claim 1 to claim 6, and configured
to obtain the distance to the distance measuring object on the
basis of a time difference of the first pulse signal and the second
pulse signal measured by the time difference measuring device.
10. A distance measuring method, comprising; emitting a measuring
wave to an object to be distance-measured; acquiring a first pulse
signal at a timing of the measuring wave emitted; detecting a
reflected wave acquired by the measuring wave reflected by the
distance measuring object; acquiring a second pulse signal at a
timing of the reflected wave detected; obtaining a distance to the
distance measuring object on the basis of a time difference from
the timing of the first pulse signal acquired to the timing of the
second pulse signal acquired; and obtaining the distance to the
distance measuring object on the basis of the time difference
between the first pulse signal and the second pulse signal acquired
by the time difference measuring method according to claim 7.
11. A time difference measuring device which measures a time
difference of two or more pulse signals generated with a
predetermined time difference, the time difference measuring device
comprising: a reference signal generation unit configured to
generate a single reference signal; an amplitude detection unit
configured to obtain amplitudes of the reference signal at
generation timings of each of the pulse signals and predetermined
delay timings corresponding to the generation timings; a phase
difference detection unit configured to calculate a phase
difference between the generation timings of the pulse signals on
the basis of each of the amplitudes of the reference signal at the
generation timings and the delay timings obtained for each of the
pulse signals, detected by the amplitude detection unit; and a time
difference calculation unit configured to calculate a generation
time difference of the two or more pulse signals, on the basis of
the phase difference detected by the phase difference detection
unit and a cycle of the reference signal.
12. A time difference measuring device according to claim 11,
wherein: the reference signal generation unit is configured to
generate a sine wave signal or a cosine wave signal as the
reference signal; and the amplitude detection unit is configured to
use the timings corresponding to the phase delays equivalent to the
odd number-times of the phase difference of .pi./2 of the reference
signal from the generation timing, as the delay timings.
13. A distance measuring device, comprising: a measuring wave
emission unit configured to emit a measuring wave to an object to
be distance-measured; a reflected wave detection unit configured to
detect a reflected wave acquired by the measuring wave reflected by
the distance measuring object; and a distance measuring unit
configured to acquire a first pulse signal at a timing of the
measuring wave emitted from the measuring wave emission unit,
acquire a second pulse signal at a timing of the reflected wave
detected by the reflected wave detection unit, and obtain a
distance to the distance measuring object on the basis of a time
difference from the timing of the first pulse signal acquired to
the timing of the second pulse signal acquired, wherein the
distance measuring unit includes the time difference measuring
device according to claim 1, and configured to obtain the distance
to the distance measuring object on the basis of a time difference
of the first pulse signal and the second pulse signal measured by
the time difference measuring device.
14. A time difference measuring device according to claim 2,
further comprising a coarse time difference detection unit
configured to detect a coarse generation time difference of the two
pulse signals, wherein the time difference calculation unit is
configured to calculate, in addition to a precise time difference
calculated on the basis of the phase difference detected by the
phase difference detection unit and the cycle of the at least two
reference signals, the generation time difference of the two pulse
signals by the coarse generation time difference detected by the
coarse time difference detection unit.
15. A time difference measuring device according to claim 2,
wherein the at least two reference signals are a sine wave signal
and a cosine wave signal.
16. A time difference measuring device according to claim 15,
wherein the phase difference detection unit is configured to:
detect an amplitude A11 of the sine wave signal and an amplitude
A12 of the cosine wave signal, at the generation timing of one
pulse signal preceding in time series of the two pulse signals;
calculate a ratio A11/A12 of the amplitudes A11, A12; calculate a
phase .theta.start on the basis of the amplitude ratio A11/A12 by
tan.sup.-1(A11/A12); detect an amplitude A21 of the sine wave
signal and an amplitude A22 of the cosine wave signal, at the
generation timing of the other pulse signal succeeding in time
series of the two pulse signals; calculate a ratio A21/A22 of the
amplitudes A21, A22; calculate a phase .theta.stop on the basis of
the amplitude ratio A21/A22 by tan.sup.-1(A21/A22); and calculate a
phase difference .DELTA..theta. of the generation timings of the
two pulse signals by (.theta.stop-.theta.start).
17. A time difference measuring device according to claim 2,
wherein the reference signal generation unit is configured to
originally generate one reference signal, generate a new reference
signal of which phase is delayed by virtually .pi./2[rad] to the
reference signal originally generated, and generate the originally
generated reference signal and the new reference signal as the two
reference signals having the phase difference of virtually
.pi./2.
18. A distance measuring method, comprising; emitting a measuring
wave to an object to be distance-measured; acquiring a first pulse
signal at a timing of the measuring wave emitted; detecting a
reflected wave acquired by the measuring wave reflected by the
distance measuring object; acquiring a second pulse signal at a
timing of the reflected wave detected; obtaining a distance to the
distance measuring object on the basis of a time difference from
the timing of the first pulse signal acquired to the timing of the
second pulse signal acquired; and obtaining the distance to the
distance measuring object on the basis of the time difference
between the first pulse signal and the second pulse signal acquired
by the time difference measuring method according to claim 8.
19. A distance measuring device, comprising: a measuring wave
emission unit configured to emit a measuring wave to an object to
be distance-measured; a reflected wave detection unit configured to
detect a reflected wave acquired by the measuring wave reflected by
the distance measuring object; and a distance measuring unit
configured to acquire a first pulse signal at a timing of the
measuring wave emitted from the measuring wave emission unit,
acquire a second pulse signal at a timing of the reflected wave
detected by the reflected wave detection unit, and obtain a
distance to the distance measuring object on the basis of a time
difference from the timing of the first pulse signal acquired to
the timing of the second pulse signal acquired, wherein the
distance measuring unit includes the time difference measuring
device according to claim 11, and configured to obtain the distance
to the distance measuring object on the basis of a time difference
of the first pulse signal and the second pulse signal measured by
the time difference measuring device.
Description
TECHNICAL FIELD
[0001] The present invention relates to a time difference measuring
device, time difference measuring method, distance measuring
device, and distance measuring method, specifically to an
improvement on the measurement of a time difference between pulse
signals having an extremely short time interval.
BACKGROUND ART
[0002] The distance measuring device representing a recent
surveying instrument emits a measuring wave such as laser beams or
microwaves to a distance measuring object, detects a reflected wave
from the distance measuring object (hereinafter, generally named as
a measuring wave), calculates a to-and-fro travel distance of the
measuring wave on the basis of a time difference between an
emission time and a detection time of the measuring wave, and
thereby calculates the distance to the distance measuring
object.
[0003] Here, the measurement of a time difference (time interval)
has been performed, for example, by generating a high frequency
clock signal having an extremely short already-known cycle, in
comparison to a time difference between an emission time of a
measuring wave and a detection time thereof, counting the clock
number of the high frequency clock signal which are generated
between the emission time and the detection time of the measuring
wave, and multiplying the counted number by the cycle. However this
measurement needs to raise the frequency of the clock signal in
order to enhance the measurement accuracy; and yet, it embraces a
limitation of raising the frequency of the clock signal.
[0004] Accordingly, a method has been developed which generates
plural high frequency clock signals mutually having predetermined
phase differences, counts the clock number of the clock signals
each, and thereby brings the frequencies of the clock signals into
high frequencies artificially. However, this method needs
measurement repetitions corresponding to the number of the
generated clock signals in enhancing the reliability of measurement
accuracy, which makes the measurement time longer and invites a
problem in practical use.
[0005] Accordingly, the present applicant has proposed a technique
which generates a start signal synchronized with an emission time
of a measuring wave and a stop signal synchronized with a detection
time thereof repeatedly plural times with predetermined time
intervals each, samples a reference signal of a sine wave or the
like generated in a shorter cycle than this repetition cycle with a
repetitive start signal, samples it with a repetitive stop signal,
calculates a phase difference of a first sampling wave acquired by
the sampling with the start signal and a second sampling wave
acquired by the sampling with the stop signal, calculates a phase
difference between the start signal and the stop signal based on
this phase difference, and converts the acquired phase difference
into a time difference (PATENT DOCUMENT 1). [0006] PATENT DOCUMENT
1: Japanese Patent Registration No. 2916780 Bulletin
DISCLOSURE OF THE INVENTION
Problems to Be Solved By the Invention
[0007] However, the above proposed technique requires generating
the start signal and the stop signal plural times and detecting the
signals plural times, which is disadvantageous to a further
speed-up of measurement.
[0008] Especially, in case of the above technique not being applied
to a distance measuring device that measures a distance to a fixed
measuring object provided with a cube corner, but being applied to
a distance measuring device intending to include a natural object
likely to be displaced by environmental influences such as a wind
in the measuring object, or being applied to a distance measuring
device that performs distance measurements to the outline of a
distance measuring object point by point to specify the whole
figure of the distance measuring object, a further shortening of
individual measuring times is demanded.
[0009] The natural object is apt to be displaced by environmental
influences; and if there occurs a displacement during repetitive
measurements, part of plural data acquired by plural measurements
include errors by the displacement, and such data deteriorate the
reliability of measurement. Therefore, such data are needed to be
excluded from an averaging calculation of those plural data and so
forth.
[0010] And in case of specifying the outline figure by scanning the
outline of an object point by point, the number of objective points
in the distance measurement increases tremendously, which requires
a long measurement time for the distance measurement of the whole
outline.
[0011] Further in the above proposed technique, plural start
signals and plural stop signals each function as the sampling
signals; the generation time interval between the start signals and
the generation time interval between the stop signals are required
to be precisely constant, and a control to maintain the generation
time interval at a constant becomes necessary as well.
[0012] The present invention has been made in view of the above
circumstances, and aims to provide a time difference measuring
device, time difference measuring method, distance measuring device
using the time difference measuring device, and distance measuring
method using the time difference measuring method, which precisely
measures the time difference of two pulse signals generated with a
predetermined time difference by one measurement without repeatedly
generating these two pulse signals.
Means for Solving the Problems
[0013] The first time difference measuring device according to the
present invention is a time difference measuring device which
measures a time difference of two or more pulse signals generated
with a predetermined time difference, the time difference measuring
device is characterized by comprising: a reference signal
generation means configured to generate one or more reference
signals; an amplitude detection means configured to obtain two
amplitudes based on the reference signals so as to be substantially
equal to sampling the reference signals, at predetermined two
timings which depend on generation timings of each of the pulse
signals; a phase difference detection means configured to calculate
a phase difference between the generation timings of the pulse
signals on the basis of each of the amplitudes of the reference
signals obtained for each of the pulse signals, detected by the
amplitude detection means; and a time difference calculation means
configured to calculate a generation time difference of the two
pulse signals on the basis of the phase difference detected by the
phase difference detection means and a cycle of the reference
signals.
[0014] Here, "obtain two amplitudes based on the reference signals
so as to be substantially equal to sampling the reference signals,
in predetermined two timings which depend on generation timings of
each of the pulse signals" means the following. When the number of
the reference signals generated by the reference signal generation
means is two, and the two reference signals have a predetermined
phase difference, for example, the one reference signal is
displaced in the amplitude to the other reference signal by a time
equivalent to the phase difference. Sampling both the reference
signals simultaneously at the predetermined timings can be
estimated substantially equal to sampling a single reference signal
at two different timings of a generation timing of the pulse signal
and another timing displaced by the time difference (equivalent to
the predetermined phase difference of the reference signal) from
the generation timing. Therefore, this means that a single
reference signal can be sampled at two different timings, or two
reference signals having a phase difference can be sampled at a
single timing.
[0015] According to the first time difference measuring device of
the invention thus constructed, the generation timings of each of
the pulse signals can be expressed as the phases in the reference
signals, on the basis of the two amplitudes that can be estimated
to be sampled at two different timings by each of the pulse
signals. The phase differences acquired by each of the pulse
signals can be expressed as the time differences of the generation
timings of the pulse signals, using the cycle of the reference
signals.
[0016] The first time difference measuring device according to the
invention is provided with the time difference calculation means
that calculates the generation time difference of the two pulse
signals on the basis of the phase difference detected by the phase
difference detection means and the cycle of the reference signals;
therefore, one-time detection of each of the reference signals at
the generation timings each of the two pulse signals will determine
the time difference between both the pulse signals, which makes a
quick measurement possible.
[0017] It is preferable to apply a sine wave signal or a cosine
wave signal, for example, to the reference signal. The reason is
that the correspondence between amplitude and phase is general.
However, the reference signal is not restricted to the sine wave
signal or cosine wave signal. Various signals can be applied, such
as a triangle wave signal, saw tooth wave signal, and so forth, as
long as the correspondence between amplitude and phase is
stipulated in advance by means of a look-up table or a function
table or the like.
[0018] The second time difference measuring device according to the
invention is a time difference measuring device which measures a
time difference of two pulse signals generated with a predetermined
time difference, the time difference measuring device is
characterized by comprising: a reference signal generation means
configured to generate at least two reference signals having a
phase difference of virtually .pi./2[rad] (including the odd
number-times of virtually .pi./2[rad] (.pi./2[rad].times.(2n-1);
n=1, 2, . . . , the same hereinafter); a phase difference detection
means configured to calculate a phase difference of generation
timings of the two pulse signals, on the basis of amplitudes of at
least the two reference signals at each of the generation timings
of the two pulse signals; and a time difference calculation means
configured to calculate a generation time difference of the two
pulse signals, on the basis of the phase difference detected by the
phase difference detection means and a cycle of the reference
signals.
[0019] Here, the two reference signals may be or may not be
synchronous with the pulse signals.
[0020] According to the second time difference measuring device
thus constructed, the phase difference detection means performs
sampling only one time at the generation timings each of the two
pulse signals generated with a time difference, to the two
reference signals having the phase difference of .pi./2[rad] that
the reference signal generation means generates, and detects the
amplitudes of the reference signals at each sampling.
[0021] Further, the phase difference detection means calculates the
phases of the reference signals at each of the timings, on the
basis of the relation of amplitude such as an amplitude difference
or an amplitude ratio between the two reference signals at each of
the timings acquired, calculates the difference of the phases each
corresponding to the two timings acquired, and calculates a
generation time difference of the two pulse signals by this phase
difference and the cycle of the reference signals.
[0022] Therefore, one-time detection of each of the reference
signals at the generation timings each of the two pulse signals
will determine the time difference between both the pulse signals,
which makes a quick measurement possible.
[0023] Applying such signals as a sine wave signal and a cosine
wave signal, of which phase difference is .pi./2[rad], to the
reference signals, calculating a ratio of directly detected values
(amplitudes), and calculating an arc tangent of the ratio will
produce a phase .theta.. Then, from the two phases thus obtained,
the phase difference .DELTA..theta. can be detected.
[0024] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signals, a constant resolution and detection sensitivity can be
acquired.
[0025] The reason is as follows. The variation of the sine wave
signal (sin .theta.) to the variation of .theta. is significant
near a position where the vibration thereof crosses the center (sin
.theta.=0) of the amplitude; therefore, a high detection
sensitivity (resolution) can be acquired when detected at this
position. In contrast, the variation of sin .theta. to the
variation of .theta. is insignificant near a peak position of the
vibration; therefore, the detection sensitivity (resolution) at
this position becomes low. On the other hand, since the cosine wave
signal has the phase difference of .pi./2[rad] to the sine wave
signal, when the detection sensitivity of the sine wave signal
becomes low, the detection sensitivity (resolution) of the cosine
wave signal becomes high. Therefore, the phase calculated by the
arc tangent based on the ratio of both is continually detected with
a high detection sensitivity and high resolution.
[0026] The second time difference measuring device according to the
invention preferably further includes a coarse time difference
detection means configured to detect a coarse generation time
difference of the two pulse signals, wherein the time difference
calculation means is configured to calculate, in addition to a
precise time difference calculated on the basis of the phase
difference detected by the phase difference detection means and the
cycle of the reference signals, a generation time difference of the
two pulse signals by the coarse generation time difference detected
by the coarse time difference detection means.
[0027] The coarse time difference detection means is only needed to
be capable of detecting a time with the resolution of virtually one
cycle of the above reference signals, to which can be applied one
that detects a coarse time difference by counting the pulse number
of the reference signals, using a well-known pulse counter and the
like.
[0028] According to the time difference measuring device provided
with such preferable construction, since the coarse generation time
difference of the two pulse signals can be detected by the coarse
time difference detection means, the generation time difference of
the two pulse signals can be measured precisely, even if the time
difference is as long as it exceeds one cycle of the reference
signals.
[0029] The reason is as follows. The phase difference
.DELTA..theta. of the reference signals corresponding to a time
difference between the two pulse signals detected by the time
difference calculation means is calculated as a value within 0[rad]
to 2.pi.[rad]. However, since the reference signals are a periodic
signal, and the phase difference .DELTA..theta. latently includes
2.pi.+.DELTA..theta., 4.pi.+.DELTA..theta., . . . , in addition to
.DELTA..theta..ltoreq.2.pi., the phase difference can be expressed
as the general formula: 2.pi.(n-1)+.DELTA..theta.(n: natural
number).
[0030] On the other hand, the generation time difference of the two
pulse signals needs to be calculated including the phase difference
2.pi. (n-1)[rad] being the first term of the above general formula
as a time; and the natural number n is required to be
specified.
[0031] Now, even if the generation time difference of the two pulse
signals exceeds one cycle (2.pi.[rad]) of the reference signal, the
coarse time difference detection means is able to detect the
generation time difference in brief with the resolution of
virtually one cycle of the reference signal. On the basis of the
generation time difference briefly detected by the coarse time
difference detection means, the phase difference 2.pi.(n-1)[rad] of
the first term of the general formula can be specified, and the
time corresponding to the phase difference as the total of the
first term and the second term ([2.pi.(n-1)+.DELTA..theta.]/2.pi.
multiplied by the periodic time [sec] of the reference signal),
that is, the generation time difference of the two pulse signals
can be obtained specifically as a unique value.
[0032] Further, in the first or the second time difference
measuring device according to the invention, it is preferable to
apply a sine wave and a cosine wave to the two reference
signals.
[0033] The combination of the sine wave (A0 sin .theta.) and the
cosine wave (A0 cos .theta.) is equivalent to the combination of
two sine waves having the phase difference of .pi./2[rad] or the
combination of two cosine waves having the phase difference of
.pi./2[rad]. These two reference signals are sampled by the pulse
signals to acquire a detected value Aij (amplitude); and the ratio
(A0 sin .theta./A0 cos .theta.) of the amplitude can be calculated
as the tangent value (tan .theta.). An inversion of the acquired
tangent value (inverse trigonometric function tan.sub.-1 .theta.
(=arctan)) will calculate the phase. Then, applying the sine and
cosine waves to the reference signals in this manner will cancel
the maximum amplitude A0 of the sine and cosine waves in the
calculation; thereby, it is possible to perform the arithmetic
processing without practically calculating the maximum amplitude
A0, which leads to simplifying the arithmetic processing.
[0034] Moreover, the variations in time of the phase calculated by
the arc tangent always become constant; therefore, regardless of
the generation timings of the two pulse signals to the reference
signals, a constant resolution and detection sensitivity can be
acquired.
[0035] In the second time difference measuring device according to
the invention, it is preferable that the phase difference detection
means is configured to detect an amplitude A11
(-A0.ltoreq.A11.ltoreq.A0) of the sine wave signal and an amplitude
A12 (-A0.ltoreq.A12.ltoreq.A0) of the cosine wave signal, at the
generation timing of one pulse signal (start signal) preceding in
time series of the two pulse signals, calculate a ratio A11/A12 of
the amplitudes A11, A12, calculate a phase .theta.start (phase of
the sine wave and cosine wave at the generation timing of the start
signal) on the basis of the amplitude ratio A11/A12 by
tan.sup.-1(A11/A12), detect an amplitude A21
(-A0.ltoreq.A21.ltoreq.A0) of the sine wave signal and an amplitude
A22 (-A0.ltoreq.A22.ltoreq.A0) of the cosine wave signal, at the
generation timing of the other pulse signal (stop signal)
succeeding in time series of the two pulse signals, calculate a
ratio A21/A22 of the amplitudes A21, A22, calculate a phase
.theta.stop (phase of the sine wave and cosine wave at the
generation timing of the stop signal) on the basis of the amplitude
ratio A21/A22 by tan.sup.-1(A21/A22), and calculate a phase
difference .DELTA..theta. of the reference signals corresponding to
a time between the generation timings of the two pulse signals by
(.theta.stop-.theta.start).
[0036] According to the time difference measuring device thus
constructed, the time difference can be calculated with high
precision by a simple arithmetic processing.
[0037] In the first or the second time difference measuring device
according to the invention, it is preferable that the reference
signal generation means is configured to originally generate one
reference signal, generate a new reference signal of which phase is
delayed by virtually .pi./2[rad] to the reference signal originally
generated, and generate the originally generated reference signal
and the new reference signal, as the two reference signals having
the phase difference of virtually .pi./2[rad].
[0038] Although the reference signal originally generated by the
reference signal generation means is only one, the originally
generated reference signal as well as the new reference signal of
which phase is delay by virtually .pi./2[rad] to the original
reference signal may be outputted as the two reference signals.
[0039] Thus, provided one is original and the other one is a
generation based on the original one, of the two reference signals,
the difference of the signal waveforms, for example, the difference
of the amplitudes are not likely to generate between the reference
signals, and the errors in calculating the phases corresponding to
the amplitudes are likely to be suppressed.
[0040] The time difference measuring method according to the
invention is A time difference measuring method which measures a
time difference of two pulse signals generated with a predetermined
time difference, the method is characterized by comprising:
detecting a coarse generation time difference of the two pulse
signals; generating a sine wave signal and a cosine wave signal
having the phase difference of virtually .pi./2 (including the odd
number-times of virtually .pi./2[rad] (.pi./2[rad].times.(2n-1);
n=1, 2, . . . , the same hereinafter) as two reference signals;
obtaining, on the basis of the amplitudes of the sine wave signal
and the cosine wave signal at each of generation timings of the two
pulse signals, a phase difference of the generation timings of the
two pulse signals; and calculating a generation time difference of
the two pulse signals, on the basis of the obtained phase
difference and a cycle of the reference signals and the coarse
generation time difference.
[0041] According to the time difference measuring method thus
constructed, the two reference signals having the phase difference
of virtually .pi./2[rad] is sampled only one time at each of the
generation timings of the two pulse signals generated with a time
difference, and the amplitudes of the reference signals are
detected at each sampling.
[0042] Further, the phases of the reference signals are calculated
at each of the timings acquired, on the basis of the relation of
amplitude such as an amplitude difference or an amplitude ratio
between the two reference signals at each of the timings, the
difference of the phases each corresponding to the two timings
acquired is calculated, and a generation time difference of the two
pulse signals is calculated by this phase difference and the cycle
of the reference signals.
[0043] Therefore, one-time detection of each of the reference
signals at the generation timings each of the two pulse signals
will determine the time difference between both the pulse signals,
which makes a quick measurement possible.
[0044] Since the reference signals are the sine wave signal and
cosine wave signal that have the phase difference of .pi./2[rad],
calculating the ratio of directly detected values (amplitudes), and
calculating the arc tangent of the ratio will produce a phase
.theta.. Then, from the two phases thus obtained, the phase
difference .DELTA..theta. can be detected.
[0045] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signals, a constant resolution and detection sensitivity can be
acquired.
[0046] By detecting the coarse generation time difference of the
two pulse signals, the generation time difference of the two pulse
signals can be measured precisely, even if the time difference is
as long as it exceeds one cycle of the reference signal.
[0047] In the time difference measuring method according to the
invention, it is preferable to detect an amplitude A11 of the sine
wave signal and an amplitude A12 of the cosine wave signal, at the
generation timing of one pulse signal preceding in time series of
the two pulse signals, to calculate a ratio A11/A12 of the
amplitudes A11, A12, to calculate a phase .theta.start on the basis
of the amplitude ratio A11/A12 by tan.sup.-1(A11/A12), to detect an
amplitude A21 of the sine wave signal and an amplitude A22 of the
cosine wave signal, at the generation timing of the other pulse
signal succeeding in time series of the two pulse signals, to
calculate a ratio A21/A22 of the amplitudes A21, A22, to calculate
a phase .theta.stop on the basis of the amplitude ratio A21/A22 by
tan.sup.-1(A21/A22), and to calculate a phase difference
.DELTA..theta. of the reference signals corresponding to a time
between the generation timings of the two pulse signals by
(.theta.stop-.theta.start).
[0048] According to the time difference measuring method with a
preferable construction, the time difference can be calculated with
high precision by a simple arithmetic processing.
[0049] The first distance measuring device according to the
invention is characterized by comprising: a measuring wave emission
means configured to emit a measuring wave to an object to be
distance-measured; a reflected wave detection means configured to
detect a reflected wave acquired by the measuring wave reflected by
the distance measuring object; and a distance measuring means
configured to acquire a first pulse signal at a timing of the
measuring wave emitted from the measuring wave emission means,
acquire a second pulse signal at a timing of the reflected wave
detected by the reflected wave detection means, and obtain a
distance to the distance measuring object on the basis of a time
difference from the timing of the first pulse signal acquired to
the timing of the second pulse signal acquired, and wherein the
distance measuring means includes the time difference measuring
device according to the present invention, and configured to obtain
the distance to the distance measuring object on the basis of a
time difference of the first pulse signal and the second pulse
signal measured by the time difference measuring device.
[0050] Here, the distance measuring device includes the so-called
surveying instrument and a figure measuring device that specifies
the outline figure of a distance measuring object by performing
distance measurements to the distance measuring object as well.
[0051] Various well-known electromagnetic waves conventionally used
as a distance measuring beam, such as microwaves, light waves
(laser beams, infrared light, etc.), etc. can be applied to a
signal wave that the measuring wave emission means emits to the
distance measuring object.
[0052] According to the first distance measuring device of the
invention thus constructed, the distance measuring means is
provided with the time difference measuring device according to the
invention; and the time difference measuring device needs to
perform one-time detection of each of the reference signals at the
generation timings each of the first and second pulse signals, so
that the time difference between both the pulse signals can be
measured quickly, and the distance measuring performance based on
the measurement of the time difference can be quickened.
[0053] Applying such signals as a sine wave signal and a cosine
wave signal, of which phase difference is .pi./2[rad], to the
reference signals, calculating a ratio of directly detected values
(amplitudes), and calculating an arc tangent of the ratio will
produce a phase .theta.. Then, from the two phases thus obtained,
the phase difference .DELTA..theta. can be detected.
[0054] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signals, a constant resolution and detection sensitivity can be
acquired.
[0055] The distance measuring method according to the invention is
characterized by comprising; emitting a measuring wave to an object
to be distance-measured; acquiring a first pulse signal at a timing
of the measuring wave emitted; detecting a reflected wave acquired
by the measuring wave reflected by the distance measuring object;
acquiring a second pulse signal at a timing of the reflected wave
detected; and obtaining a distance to the distance measuring object
on the basis of a time difference from the timing of the first
pulse signal acquired to the timing of the second pulse signal
acquired, and wherein the distance to the distance measuring object
is obtained on the basis of the time difference between the first
pulse signal and the second pulse signal acquired by the time
difference measuring method according to the present invention.
[0056] According to the distance measuring method of the invention
thus constructed, only one-time detection of each of the reference
signals at the generation timings each of the first and second
pulse signals, by the aforementioned time difference measuring
method, will quickly measure the time difference between both the
pulse signals; therefore, the distance measuring performance based
on the measurement of the time difference can be quickened.
[0057] Applying such signals as a sine wave signal and a cosine
wave signal, of which phase difference is .pi./2[rad], to the
reference signals, calculating a ratio of directly detected values
(amplitudes), and calculating an arc tangent of the ratio will
produce a phase .theta.. Then, from the two phases thus obtained,
the phase difference .DELTA..theta. can be detected.
[0058] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signals, a constant resolution and detection sensitivity can be
acquired.
[0059] The third time difference measuring device according to the
present invention is a time difference measuring device which
measures a time difference of two or more pulse signals generated
with a predetermined time difference, the time difference measuring
device is characterized by comprising: a reference signal
generation means configured to generate a single reference signal;
an amplitude detection means configured to obtain amplitudes of the
reference signal at generation timings of each of the pulse signals
and predetermined delay timings corresponding to the generation
timings; a phase difference detection means configured to calculate
a phase difference between the generation timings of the pulse
signals on the basis of each of the amplitudes of the reference
signal at the generation timings and the delay timings obtained for
each of the pulse signals, detected by the amplitude detection
means; and a time difference calculation means configured to
calculate a generation time difference of the two pulse signals, on
the basis of the phase difference detected by the phase difference
detection means and a cycle of the reference signal.
[0060] According to the time difference measuring device thus
constructed, the amplitude detection means samples a single
reference signal generated by the reference signal generation means
at the generation timings of the pulse signals and at a timing
corresponding to a phase difference equivalent to the predetermined
delay timings from the generation timings, and detects the
amplitudes of the reference signal corresponding to each of the
timings.
[0061] Further, the phase difference detection means is configured
to calculate the phase of the reference signal at the generation
timing of one pulse signal on the basis of the relation of
amplitude such as an amplitude difference or an amplitude ratio
between the two reference signals at each of the timings acquired,
calculate in the same manner the phase of the reference signal at
the generation timing of the other pulse signal, calculate the
difference of the two phases acquired, and calculate a generation
time difference of the two pulse signals by this phase difference
and the cycle of the reference signal.
[0062] Therefore, one-time detection of the reference signal at
each of the generation timings and delay timings of the two pulse
signals will determine the time difference between both the pulse
signals, which makes a quick measurement possible.
[0063] Applying a sine wave signal and a cosine wave signal to the
reference signal, for example, applying the timings corresponding
to the phase delays equivalent to the phase difference of
.pi./2[rad] of the reference signal (including the odd number-times
of virtually .pi./2[rad] (.pi./2[rad].times.(2n-1); n=1, 2, . . .
), the same hereinafter) to the delay timings, calculating the
ratio of directly detected values (amplitudes) at the generation
timings and the delay timings of each of the pulse signals, and
calculating the arc tangent of the ratio will produce a phase
.theta. of each of the pulse signals. Then, from the two phases
thus obtained, the phase difference .DELTA..theta. can be
detected.
[0064] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signal, a constant resolution and detection sensitivity can be
acquired.
[0065] The reason is as follows. The variation of the sine wave
signal (sin .theta.) to the variation of .theta., for example, is
significant near a position where the vibration thereof crosses the
center (sin .theta.=0) of the amplitude, and a high detection
sensitivity (resolution) can be acquired when detected at this
position. In contrast, the variation of sin .theta. to the
variation of .theta. is insignificant near a peak position of the
vibration, and the detection sensitivity (resolution) at this
position becomes low. The delay timings, on the other hand, assume
the phase difference of .pi./2[rad] from the phase equivalent to
that near the peak position of the vibration; and the vibration
thereof is equivalent to that near a position of crossing the
center (sin .theta.=0) of the amplitude, and a high detection
sensitivity (resolution) is acquired. Therefore, the phase
calculated by the arc tangent based on the ratio of each of the
amplitudes detected at the generation timings and delay timings is
continually detected with a high detection sensitivity and high
resolution.
[0066] The second distance measuring device according to the
invention is characterized by comprising: a measuring wave emission
means configured to emit a measuring wave to an object to be
distance-measured; a reflected wave detection means configured to
detect a reflected wave acquired by the measuring wave reflected by
the distance measuring object; and a distance measuring means
configured to acquire a first pulse signal at a timing of the
measuring wave emitted from the measuring wave emission means,
acquire a second pulse signal at a timing of the reflected wave
detected by the reflected wave detection means, and obtain a
distance to the distance measuring object on the basis of a time
difference from the timing of the first pulse signal acquired to
the timing of the second pulse signal acquired, and wherein the
distance measuring means includes the time difference measuring
device according to the present invention, and configured to obtain
the distance to the distance measuring object on the basis of a
time difference of the first pulse signal and the second pulse
signal measured by the time difference measuring device.
[0067] Here, the distance measuring device includes the so-called
surveying instrument and a figure measuring device that specifies
the outline figure of a distance measuring object by performing
distance measurements to the distance measuring object as well.
[0068] Various well-known electromagnetic waves conventionally used
as a distance measuring beam, such as microwaves, light waves
(laser beams, infrared light, etc.), etc. can be applied to a
signal wave that the measuring wave emission means emits to the
distance measuring object.
[0069] According to the second distance measuring device of the
invention thus constructed, the distance measuring means is
provided with the aforementioned time difference measuring device
according to the invention; and the time difference measuring
device only needs to perform one-time detection of the reference
signal at each of the generation timings and delay timings of the
first and second pulse signals, so that the time difference between
both the pulse signals can be measured quickly, and the distance
measuring performance based on the measurement of the time
difference can be quickened.
[0070] Applying a sine wave signal or a cosine wave signal to the
reference signal, for example, applying virtually .pi./2[rad] to
the phase difference corresponding to a time between the generation
timing and the delay timing, calculating the ratio of directly
detected values (amplitudes), and calculating the arc tangent of
the ratio will produce a phase .theta.. Then, from the two phases
thus obtained, the phase difference .DELTA..theta. can be
detected.
[0071] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signal, a constant resolution and detection sensitivity can be
acquired.
EFFECT OF THE INVENTION
[0072] According to the time difference measuring device and the
time difference measuring method of the invention, one-time
detection of each of the reference signals at the generation
timings each of the two pulse signals or one-time detection of the
reference signal at each of the generation timings and delay
timings of the two pulse signals will determine the time difference
between both the pulse signals, and the distance measuring
performance can be quickened.
[0073] According to the distance measuring device and the distance
measuring method of the invention, the distance measuring means is
provided with the aforementioned time difference measuring device
according to the invention; and the time difference measuring
device only needs to perform one-time detection of each of the
reference signals at the generation timings each of the first and
second pulse signal, or to perform one-time detection of the
reference signal at each of the generation timings and the delay
timings of the two pulse signals, so that the time difference
between both the pulse signals can be measured quickly. Thereby,
the distance measurement based on this time difference measurement
can be quickened.
BRIEF DESCRIPTION OF THE DRAWINGS
[0074] FIG. 1 is a block diagram illustrating a surveying device
including the time difference measuring device according to one
embodiment of the present invention;
[0075] FIG. 2 is a chart explaining the principle of time
difference measurement;
[0076] FIG. 3 is a chart illustrating a concrete optical system of
the surveying device illustrated in FIG. 1;
[0077] FIG. 4 is a chart illustrating a concrete control system
(with synchronization) of the surveying device illustrated in FIG.
1;
[0078] FIG. 5 is a chart illustrating a concrete control system
(without synchronization) of the surveying device illustrated in
FIG. 1;
[0079] FIG. 6 is a chart illustrating a modified example of the
control system of FIG. 4 wherein a reference signal generation unit
generates only a sine wave signal as one reference signal, and the
other reference signal is generated on the basis of the generated
sine wave signal;
[0080] FIG. 7 is a block diagram illustrating a surveying device
including the time difference measuring device according to another
embodiment of the present invention;
[0081] FIG. 8 is a chart explaining the principle of time
difference measurement;
[0082] FIG. 9 is a chart illustrating a concrete control system
(with synchronization) of the surveying device illustrated in FIG.
7; and
[0083] FIG. 10 is a chart illustrating a concrete control system
(without synchronization) of the surveying device illustrated in
FIG. 7.
EXPLANATION OF THE REFERENCE NUMERALS
[0084] 10: Measuring light emission means (measuring wave emission
means) [0085] 11: PLD (light source) [0086] 20: Reflected light
detection means (reflected wave detection means) [0087] 21: Photo
detection element [0088] 30: Distance measuring means [0089] 40:
Time difference measuring device [0090] 90: Distance measuring
object [0091] 100: Surveying device (distance measuring device)
[0092] L1: Laser beam [0093] L2: Reflected laser beam [0094] M1:
Start signal (first pulse signal) [0095] M2: Stop signal (second
pulse signal) [0096] S1, S2: Reference signal [0097] A11, A12, A21,
A22: Amplitude
BEST MODE FOR CARRYING OUT THE INVENTION
[0098] The best modes of the time difference measuring device, time
measuring method, distance measuring device, and distance measuring
method according to the invention will now be described with
reference to the appended drawings.
EMBODIMENT 1
[0099] FIG. 1 is a block diagram illustrating the construction of a
surveying device 100 being one embodiment of a distance measuring
device according to the invention, which includes a time difference
measuring device of the invention as a part of a distance measuring
means.
[0100] The surveying device 100 illustrated in FIG. 1 includes a
measuring light emission means 10 (measuring wave emission means)
that emits a pulse laser beam L1 as a measuring wave to a distance
measuring object 90, a reflected light detection means 20
(reflected wave detection means) that detects a reflected laser
beam L2 (reflected wave) acquired by the laser beam L1 reflecting
on the distance measuring object 90, a distance measuring means 30,
and a distance measurement result output unit 50. Here, the
distance measuring means 30 outputs a pulse start signal M1 (first
pulse signal) at a timing of the laser beam L1 being emitted from
the measuring light emission means 10, outputs a pulse stop signal
M2 (second pulse signal) at a timing of the reflected laser beam L2
being detected by the reflected light detection means 20, and
calculates a distance to the distance measuring object 90 on the
basis of a time difference .DELTA.t from the timing of the start
signal M1 being outputted to the timing of the stop signal M2 being
outputted. Then, the distance measurement result output unit 50
outputs the result of this distance measurement in a visible
form.
[0101] The measuring light emission means 10 includes a
semiconductor laser (PLD) 11 being a light source that emits the
pulse laser beam L1, and an emission optical system 12 including
lenses and so forth that guide the laser beam L1 emitted from the
PLD 11 toward the distance measuring object 90. The laser beam L1
emitted from the PLD 11 has a comparably high peak power, and is a
pulse laser beam of which duty ratio is about 0.01%.
[0102] The reflected light detection means 20 includes a
photo-detection element 21 that detects the reflected laser beam
L2, and a detection optical system 22 that guides the reflected
laser beam L2 to the photo-detection element 21. Here, the
photo-detection element 21 may be any element that is capable of
detecting the pulse reflected laser beam L2, for which can be used
an avalanche photo-diode (APD), for example.
[0103] The distance measuring means 30 includes a time difference
measuring device 40 that measures an output time difference
.DELTA.t between the two pulse signals M1, M2 that are internally
outputted at a detection timing of the laser beam L1 and a
detection timing of the reflected laser beam L2, and a distance
conversion unit 31 that converts the measured time difference
.DELTA.t into the distance and outputs the result.
[0104] The time difference measuring device 40 internally generates
the above two pulse signals M1, M2. Further, the time difference
measuring device 40 includes a reference signal generation unit 41
(reference signal generation means) that generates two reference
signals S1, S2, of which phase difference is .pi./2, a phase
difference detection unit 42 (phase difference detection means), a
coarse time difference detection unit 43 (coarse time difference
detection means) that detects a coarse time difference "ta" between
the generation timings of the two pulse signals M1, M2 each, and a
time difference calculation unit 44 (time difference calculation
means). Here, the phase difference detection unit 42 calculates a
phase difference .DELTA..theta. of the reference signal S1 (or
reference signal S2) between the generation timings of the two
pulse signals M1, M2 each, on the basis of an amplitude A11
(amplitude of the reference signal S1 at the generation timing of
the start signal M1), an amplitude A12 (amplitude of the reference
signal S2 at the generation timing of the start signal M1), an
amplitude A21 (amplitude of the reference signal S1 at the
generation timing of the stop signal M2), and an amplitude A22
(amplitude of the reference signal S2 at the generation timing of
the stop signal M2). Then, the time difference calculation unit 44
calculates a generation time difference .DELTA.t of the start
signal M1 and the stop signal M2, on the basis of the phase
difference .DELTA..theta. detected by the phase difference
detection unit 42, a cycle Ts of the reference signals S1, S2, and
the coarse time difference ta detected by the coarse time
difference detection unit 43.
[0105] As the reference signals S1, S2 in this embodiment, a sine
wave signal (A0 sin .theta.; A0 represents the maximum amplitude)
is applied to the reference signal S1, and a cosine wave signal (A0
cos .theta.) is applied to the reference signal S2, which is
equivalent to a sine wave signal (A0 sin (.theta.+.pi./2)) having
the phase difference of .pi./2 to the sine wave reference signal
S1, for example. However, the reference signals S1, S2 are not
restricted to the combination of the sine wave and cosine wave
signals, and any combinations of the other signals may be used,
provided that the reference signals S1, S2 are of two periodic
functions mutually having the phase difference of .pi./2.
[0106] The coarse time difference detection unit 43 is only needed
to be capable of detecting a time with the resolution of about one
cycle Ts of the reference signals S1, S2, to which can be applied
one that detects a coarse time difference ta (=Pc.times.Ts) by
counting the pulse number Pc of the reference signal S1 or S2 using
a well-known pulse counter or the like, for example.
[0107] The distance measurement result output unit 50 may be a
display device such as a monitor that delivers display outputs or a
printer that delivers print outputs, provided that it outputs a
distance measurement result in a visible form.
[0108] Next, the calculation principle of the generation time
difference .DELTA.t between the start signal M1 and the stop signal
M2 by the time difference measuring device 40 of the surveying
device 100 in this embodiment will be described with reference to
FIG. 2.
[0109] In the first place, the reference signal generation unit 41
of the time difference measuring device 40 generates a sine wave
signal S1 illustrated in FIG. 2(b) and a cosine wave signal S2
illustrated in FIG. 2(c).
[0110] Next, the time difference measuring device 40 generates the
start signal M1 illustrated in FIG. 2(a) at an emission timing of
the laser beam L1 from the PLD 11, and the phase difference
detection unit 42 samples and holds both the reference signals S1,
S2 by the start signal M1. The amplitudes A11, A12 of the reference
signals S1, S2 acquired by sampling and holding are illustrated in
FIG. 2(d), and they are expressed as follows, using the phase
.theta.start from the generation time of these reference
signals.
A11=A0 sin .theta.start (1)
A12=A0 cos .theta.start (2)
Consequently,
A11/A12=tan .theta.start (3)
Therefore, the phase difference detection unit 42 calculates the
phase .theta.start of the reference signals S1, S2 at the
generation time of the start signal M1, by
.theta.start=tan.sup.-1(A11/A12) (4)
The phase difference detection unit 42 temporarily stores this
calculation result in a storage area not illustrated.
[0111] Further, the time difference measuring device 40 generates
the stop signal M2 illustrated in FIG. 2(a) at a detection timing
of the reflected laser beam L2 by the photo-detection element 21,
and the phase difference detection unit 42 samples and holds both
the reference signals S1, S2 by the stop signal M2. The amplitudes
A21, A22 of the reference signals S1, S2 acquired by sampling and
holding are illustrated in FIG. 2(d), and they are expressed as
follows, using the phase .theta.stop from the generation time of
these reference signals.
A21=A0 sin .theta.stop (5)
A22=A0 cos .theta.stop (6)
Consequently,
A21/A22=tan .theta.stop (7)
Therefore, the phase difference detection unit 42 calculates the
phase .theta.stop of the reference signals S1, S2 at the generation
time of the stop signal M2, by
.theta.stop=tan.sup.-1(A21/A22) (8)
The phase difference detection unit 42 temporarily stores this
calculation result in a storage area not illustrated.
[0112] Then, the phase difference detection unit 42 reads out the
two phases .theta.start, .theta.stop stored in the storage area,
and calculates the phase difference .DELTA..theta. of the reference
signals S1, S2 corresponding to the time difference between the
generation time of the start signal M1 and the generation time of
the stop signal M2 by
.DELTA..theta.=.theta.stop-.theta.start (9)
[0113] When the generation time difference .DELTA.t of both the
pulse signals M1, M2 is shorter than the one cycle Ts of the
reference signals S1, S2, the generation time difference .DELTA.t
of both the pulse signals M1, M2 can be calculated on the basis of
the above phase difference .DELTA..theta. and the cycle Ts, by
.DELTA.t=(A.theta./2.pi.)Ts (10)
[0114] Here, the phase difference .DELTA..theta. that the phase
difference detection unit 42 calculates by the formula (9) takes a
value within 0[rad] to 2.pi.[rad]. Since the reference signals S1,
S2 are a periodic signal, the calculated phase difference
.DELTA..theta. latently includes 2.pi.+.DELTA..theta.,
4.pi.+.DELTA..theta., . . . , in addition to
.DELTA..theta..ltoreq.2.pi., and it can be expressed as the general
formula: 2.pi.(n-1)+.DELTA..theta. (n: natural number).
[0115] On the other hand, as the generation time difference
.DELTA.t of both the pulse signals M1, M2 to be calculated, the
phase difference 2.pi.(n-1)[rad] being the first term of the above
general formula needs to be converted as well, and the natural
number n is required to be specified.
[0116] Accordingly, even if the generation time difference .DELTA.t
of both the pulse signals M1, M2 exceeds a time equivalent to one
cycle (2.pi.[rad]) of the reference signals S1, S2, the coarse time
difference detection unit 43 detects the time difference .DELTA.t
in brief with the resolution of about one cycle of the reference
signals S1, S2.
[0117] Then, referring to the coarse time difference ta detected by
the coarse time difference detection unit 43, the time difference
calculation unit 44 selects the time difference .DELTA.t most
approximate to the coarse time difference ta as the time difference
to be determined, among the time differences .DELTA.t
(.DELTA..theta./2.pi.)Ts) by the formula (10) corresponding to the
phase differences .DELTA..theta. (={.DELTA..theta.,
2.pi.+.DELTA..theta., 4.pi.+.DELTA..theta., . . . ,
2.pi.(n-1)+.DELTA..theta., . . . }) detected by the phase
difference detection unit 42.
[0118] According to the above arithmetic operation, the time
difference measuring device 40 of the surveying device 100 in this
embodiment calculates the generation time difference .DELTA.t of
the start signal M1 and the stop signal M2.
[0119] Then, the distance conversion unit 31 of the distance
measuring means 30 calculates a distance D to the distance
measuring object 90 on the basis of the time difference 66 t
measured by the time difference measuring device 40, by the
following formula (11). Here, the constant c in the formula (11)
represents the speed of light [m/sec].
D=c.DELTA.t/2 (11)
[0120] The distance D to the distance measuring object 90 thus
measured is outputted by the distance measurement result output
unit 50, so that a user of the surveying device 100 can grasp the
distance D.
[0121] Here, the distance measurement result output unit 50 is a
display device or the like that displays the measured distance D to
the distance measuring object 90 as numeric information, however it
may display various setting information on the surveying device 100
and so forth, in addition to the distance D.
[0122] According to the time difference measuring device 40 and
surveying device 100 in this embodiment, only one-time detection of
each of the reference signals S1, S2 at the generation timings each
of a pair of the start signal M1 and the stop signal M2 will
accurately determine the generation time difference between both
the signals M1, M2, thus leading to quickening the measurement of a
time difference and distance.
[0123] By applying a sine wave signal and a cosine wave signal of
which phase difference is .pi./2 to the reference signals S1, S2,
calculating directly detected values (amplitudes) and calculating
an arc tangent of a ratio of the amplitudes will produce a phase
.theta., and two phases thus obtained will give a phase difference
.DELTA..theta..
[0124] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signals, a constant resolution and detection sensitivity can be
acquired.
[0125] Here, the construction illustrated in FIG. 3 can be applied
to the measuring light emission means 10 and the reflected light
detection means 20.
[0126] The optical system illustrated here assumes a construction
wherein part of the functions of the emission optical system 12 and
the detection optical system 22 are used for both, which includes a
mirror 14 that reflects the laser beam L1 emitted from the PLD 11
and guides it to the photo-detection element (APD) 21, a prism 13
that guides the laser beam L1 to the distance measuring object 90
as well as guides the reflected laser beam L2 from the distance
measuring object 90 to the photo-detection element 21, and a lens
15.
[0127] The construction illustrated here is only an example, and
the time difference measuring device and the distance measuring
device according to the invention are not limited to this
construction.
[0128] Further, as an example, the construction illustrated in FIG.
4 can be applied to a concrete control system of the time
difference measuring device 40.
[0129] In the control system illustrated, an oscillator (TXCO) 41a
outputs a pulse signal of 15 MHz, based on which a sine wave
generator (Sin) 41b and a cosine wave generator (Cos) 41c each
generates a sine wave reference signal S1 and a cosine wave
reference signal S2, of which phases are mutually shifted by
.pi./2. The sine wave reference signal S1 and the cosine wave
reference signal S2 pass bandwidth limitations by corresponding
band-pass filters (BPF) 42b, 42b. The photo-detection element (APD)
21 detects the laser beam L1 and the reflected laser beam L2, based
on which a pulse detector (Puls Det) 42a generates the start signal
M1 and the stop signal M2. At the generation timings of the start
signal M1 and the stop signal M2, A/D converters (A/D) 42c, 42c
each samples and holds the reference signals S1, S2 subjected to
the bandwidth limitations. The sampled/held values, that is, the
amplitudes A11, A12, A21, and A22 are inputted to a CPU 44a.
[0130] On the other hand, the output pulse from the oscillator 41a
is inputted to the pulse counter (CNTR) 43a. The pulse counter 43a
counts the pulse number of the output pulse inputted between the
two generation timings of the start signal M1 and the stop signal
M2 generated by the pulse detector 42a. The counted result is
inputted to the CPU 44a, which is provided for the calculation of
the coarse time difference ta by the CPU 44a. A memory (RAM) 44b
connected to the CPU 44a stores calculation results and various
constants.
[0131] The time difference measuring device and the distance
measuring device according to the invention is one that only
one-time detection of each of the two pulse signals generated with
a time difference accurately determines the time difference between
these two pulse signals; however, in a practical measurement, it is
preferable to measure plural times, to calculate the averages and
standard deviations, etc. of the plural measurement results, and to
enhance the reliability of measurement.
[0132] Now, the control system illustrated in FIG. 4 is constructed
to output the start signal M1 plural times so that the output pulse
from the oscillator 41a being a source of generating the reference
signals S1, S2 synchronizes with the start signal M1 at each
predetermined cycle of the output pulse (the phase difference
thereof becomes zero).
[0133] Since the reference signal S1 (or reference signal S2) is
synchronous with the output pulse from the oscillator 41a, the
reference signal S1 and the start signal M1 are synchronized at
each predetermined cycle of the reference signal S1 by this control
system.
[0134] Here, in this control system, the 99.sup.th cycle of the
reference signal S1 and the 100.sup.th cycle of the start signal M1
are set to become synchronous.
[0135] That is, a first frequency divider (Divider) 11a applies
1/99 frequency dividing to the output pulse from the oscillator
41a, and the frequency of the output pulse becomes 151.51 kHz. This
frequency is multiplied by 100 by a synthesizer (SYH) 11b to become
15.151 MHz, thus the 100.sup.th cycle becomes synchronous with the
99.sup.th cycle of the output pulse of 15 MHz in the phase
difference zero.
[0136] Further, a second frequency divider (Div) 11c applies
1/(23.times.77) frequency dividing to the signal of 15.151 MHz
being the result of multiplication by the synthesizer 11b. This
frequency-divided output pulse is inputted to a driver (DRIVER)
11d, and the driver 11d drives the PLD 11 to output the pulse laser
beam L1.
[0137] Thus, the PLD 11 repeatedly emits the pulse laser beam L1
with the frequency of about 8.5 kHz. Along with the repeated
emissions of the laser beam L1, the reflected laser beam L2 is
repeatedly detected, which makes it possible to measure multiple
times the time difference between the start signal M1 and the stop
signal M2. Thus, the reliability of measurement can be enhanced
through measurements by multiple times.
[0138] In the control system illustrated in FIG. 4, the reference
signal S1 (or reference signal S2) and the start signal M1 are made
up to be synchronous; however, these signals are not necessarily to
be synchronous. Both the signals S1 (or S2), M1 may be not
completely synchronous, that is, completely asynchronous, which
depend on only the signals outputted individually from mutually
independent two oscillators, and do not depend mutually, as
illustrated in FIG. 5, for example.
[0139] In the control system illustrated in FIG. 5, the control
system that generates the reference signals S1, S2 is completely
independent from the control system that emits the laser beam L1
from the PLD 11. The control system that generates the reference
signals S1, S2 is the same as the control system illustrated in
FIG. 4. On the other hand, the control system that emits the laser
beam L1 from the PLD 11 depends on an output pulse from an
oscillator (OSC) 11e being completely independent from the
oscillator 41a. A frequency divider (Div) 11f applies frequency
dividing to the output pulse outputted from the oscillator 11e;
based on the frequency-divided output pulse, a driver (DRIVER) 11g
drives the PLD 11. Thus, the laser beam L1 is emitted from the PLD
11 at a totally independent timing from the generation timings of
the reference signals S1, S2.
[0140] The time difference measuring device and the distance
measuring device having the control system thus constructed are
able to enhance the reliability of measurement by measuring plural
times.
[0141] This embodiment applies a semiconductor laser to the light
source of the surveying device in the above description; however,
the surveying device according to the invention is not restricted
to the mode of the light source. A light source that emits the
other type of laser beam, a light source that emits light other
than a laser beam, and a measuring wave emission source that
generates a measuring wave such as a microwave other than light,
etc. can be applied. When any of these is applied, the case
exhibits the same function and effect as this embodiment.
[0142] Now, based on the amplitudes A11, A12 being the actually
detected values can be calculated the phase .theta.start, and based
on the amplitudes A21, A22 can be calculated the phase .theta.stop.
However, if the reference signals S1, S2 are generated in a
condition that the maximum amplitudes A0 of both the reference
signals S1, S2 are not completely identical, an error will be
generated between the calculated phase start and a phase
.theta.start', which is calculated by an actually measured value
A0' of the maximum amplitude of the reference signal S1, the
detected amplitude A11, an actually measured value A0'' of the
maximum amplitude of the reference signal S2, and the detected
amplitude A12. Thereby, the circle of the radius A0 as illustrated
in FIG. 2(d) will be deformed into an ellipse. In the same manner,
an error will be generated between the calculated phase .theta.stop
and a phase .theta.stop', which is calculated by an actually
measured value A0' of the maximum amplitude of the reference signal
S1, the detected amplitude A21, an actually measured value A0'' of
the maximum amplitude of the reference signal S2, and the detected
amplitude A22; and the circle of the radius A0 is deformed into an
ellipse.
[0143] Even when there occurs such an error, measuring plural times
will shift the phase .theta.start and the phase .theta.stop
gradually at each time of the measurements to rotate the ellipse.
This rotation displays a self-calibration function, which dissolves
the error of measured values by the measurements plural times.
MODIFIED EXAMPLE
[0144] The aforementioned embodiment 1 is configured such that the
reference signal generation unit 41 generates one reference signal
S1 of a sine wave signal and the other reference signal S2 of a
cosine wave signal each separately and outputs the reference
signals S1, S2 each separately, as shown in FIG. 4. However, a
configuration as illustrated in FIG. 6, for example, can be applied
to a modified example, wherein the reference signal generation unit
41 is not provided with the cosine wave generator (Cos) 41c, and is
provided with a delay circuit 42d that applies processing to delay
the sine wave reference signal S1 generated by the sine wave
generator (Sin) 41b, by a time equivalent to the phase difference
90 /2[rad] (.pi./2[rad].times.(2n-1); n=1, 2, . . . ) of the
reference signal S1.
[0145] Originally, the reference signal generation unit 41
generates only one reference signal (sine wave signal) S1, and the
delay circuit 42d generates a new reference signal with the phase
of the originally generated reference signal S1 delayed by
.pi./2[rad].
[0146] The newly generated reference signal has the phase
difference of .pi./2[rad] to the reference signal, that is, the
sine wave signal, and this signal is a cosine wave signal.
[0147] Since the sine wave signal and the cosine wave signal are
outputted, the modified example achieves substantially the same
function and effect as those of the embodiment 1.
[0148] Of the two reference signals, one is original and the other
is a generation based on the original in this manner, a difference
of the signal waveforms such as a difference of the amplitudes
between both the reference signals is hard to occur. Accordingly,
the error in calculating the phases corresponding to the amplitudes
can be restrained.
EMBODIMENT 2
[0149] FIG. 7 is a block diagram illustrating the construction of a
surveying device 100' being one embodiment of a distance measuring
device according to the invention, which includes a time difference
measuring device of the invention as a part of a distance measuring
means.
[0150] The surveying device 100' illustrated in FIG. 7 includes a
measuring light emission means 10 (measuring wave emission means)
that emits a pulse laser beam L1 as a measuring wave to a distance
measuring object 90, a reflected light detection means 20
(reflected wave detection means) that detects a reflected laser
beam L2 (reflected wave) acquired by the laser beam L1 reflecting
on the distance measuring object 90, a distance measuring means
30', and a distance measurement result output unit 50. Here, the
distance measuring means 30' outputs a pulse start signal M1 (first
pulse signal) at a timing of the laser beam L1 being emitted from
the measuring light emission means 10, outputs a pulse stop signal
M2 (second pulse signal) at a timing of the reflected laser beam L2
being detected by the reflected light detection means 20, and
calculates a distance to the distance measuring object 90 on the
basis of a time difference .DELTA.t from the timing of the start
signal M1 being outputted to the timing of the stop signal M2 being
outputted. Then, the distance measurement result output unit 50
outputs the result of this distance measurement in a visible
form.
[0151] The components except the distance measuring means 30' are
the same as those to which the same symbols are given in the
surveying device 100 of the embodiment 1 illustrated in FIG. 1; and
the description thereof will be omitted.
[0152] The reflected light detection means 20 includes a
photo-detection element 21 that detects the reflected laser beam
L2, and a detection optical system 22 that guides the reflected
laser beam L2 from the measuring distance object 90 to the
photo-detection element 21. Here, the photo-detection element 21
may be any element that is capable of detecting the pulse reflected
laser beam L2, for which can be used an avalanche photo-diode
(APD), for example.
[0153] The distance measuring means 30' includes a time difference
measuring device 40' that measures an output time difference
.DELTA.t between the two pulse signals M1, M2 that are internally
outputted at a detection timing of the laser beam L1 and a
detection timing of the reflected laser beam L2, and a distance
conversion unit 31 that converts the measured time difference
.DELTA.t into the distance and outputs the result.
[0154] The time difference measuring device 40' internally
generates the above two pulse signals M1, M2. Further, the time
difference measuring device 40' includes a reference signal
generation unit 41' (reference signal generation means) that
generates a single reference signal S3, an amplitude detection unit
45', a phase difference detection unit 42' (phase difference
detection means), a coarse time difference detection unit 43
(coarse time difference detection means) that detects a coarse time
difference "ta" between the generation timings of the two pulse
signals M1, M2 each, and a time difference calculation unit 44
(time difference calculation means). Here, the amplitude detection
unit 45' that detects an amplitude A11' (amplitude of the reference
signal S3 at a generation timing t1 of the start signal M1), A12'
(amplitude of the reference signal S3 at a delay timing t1' of the
start signal M1), A21' (amplitude of the reference signal S3 at a
generation timing t2 of the stop signal M2), and A22' (amplitude of
the reference signal S3 at a delay timing t2' of the stop signal
M2), wherein the delay timing t1' is delayed by a time .DELTA.t1
equivalent to .pi./2[rad] of the phase of the reference signal S3
from the generation timing t1 of the start signal M1
(t1'=t1+.DELTA.t1), and the delay timing t2' is delay by a time
.DELTA.t2 (=.DELTA.t1=Ts/4; Ts represents the cycle of the
reference signal S3) from the generation timing t2 of the stop
signal M2, (t2'=t2+.DELTA.t2). The phase difference detection unit
42' calculates a phase .theta.start and a phase .theta.stop in the
reference signal S3, corresponding to the generation timings t1, t2
of the two pulse signals M1, M2, and using these phases
.theta.start, .theta.stop, calculates a phase difference
.DELTA..theta. (=.theta.stop-.theta.start) in the reference signal
S3, corresponding to the time difference between the generation
timings t1, t2 of the pulse signals M1, M2, on the basis of each
pair (A11' and A12'), (A21' and A22') of the amplitudes A11', A21'
at the generation timings t1, t2 and the amplitudes A12', A22' at
the delay timings t1', t2' of each of the pulse signals M1, M2. And
the time difference calculation unit 44 calculates a generation
time difference .DELTA.t of the start signal M1 and the stop signal
M2, on the basis of the phase difference .DELTA..theta. detected by
the phase difference detection unit 42', a cycle Ts of the
reference signal S3, and the coarse time difference ta detected by
the coarse time difference detection unit 43.
[0155] The reference signal S3 in this embodiment is a sine wave
signal (A0 sin .theta.; A0 represents the maximum amplitude), for
example, and it may be a cosine wave signal (A0 cos .theta.).
[0156] The delay times .DELTA.t1, .DELTA.t2 (=Ts/4) set by the
amplitude detection unit 45' are equivalent to the phase difference
of .pi./2[rad] in the reference signal S3, however they may be a
time equivalent to the phase difference of the odd number-times of
.pi./2[rad] (.pi./2[rad].times.(2n-1); n=1, 2, . . . ) in the
reference signal S3.
[0157] Next, the calculation principle of the generation time
difference .DELTA.t between the start signal M1 and the stop signal
M2 by the time difference measuring device 40' of the surveying
device 100' in this embodiment will be described with reference to
FIG. 8.
[0158] First, the reference signal generation unit 41' of the time
difference measuring device 40' generates a sine wave signal S3
illustrated in FIG. 8(b).
[0159] Next, the time difference measuring device 40' generates the
start signal M1 illustrated in FIG. 8 (a) at an emission timing of
the laser beam L1 from the PLD 11; the amplitude detection unit 45'
samples/holds the reference signal S3 at the generation timing t1
of the start signal M1 and detects the amplitude A11' of the
reference signal S3 at the generation timing t1.
[0160] Further, the amplitude detection unit 45' applies processing
to delay the start signal M1 by the time .DELTA.t1 equivalent to
the phase .pi./2[rad] of the reference signal S3 from the
generation timing t1, generates a same pulse signal M1' as the
start signal M1 at the delay timing t1' (=t1+.DELTA.t1),
samples/holds the reference signal S3 by the pulse signal M1'
generated at the delay timing t1', and detects the amplitude A12'
of the reference signal S3 at the delay timing t1'.
[0161] Here, The amplitudes A11', A12' of the reference signal S3
acquired by sampling and holding can be expressed as follows, using
the phase .theta.start from the generation time of the reference
signal S3.
A11'=A0 sin .theta.start (1')
A12'=A0 sin(.theta.start+.pi./2) (2')
Here, .theta.start=2.pi.(t1/Ts), using the cycle Ts of the
reference signal S3.
[0162] Here, the formula (2') can be transformed into the
following:
A12'=A0 cos .theta.start (2'')
The formulas (1') and (2'') show that taking the amplitude A11' at
the generation timing t1 of the start signal M1 on the vertical
axis and taking the amplitude A12' at the generation timing t1' of
the start signal M1 on the horizontal axis will locate the
intersection of both the amplitudes A11', A12' on the same
circumference of a circle as FIG. 2(d), as illustrated in FIG.
8(c).
[0163] The ratio A11'/A12' of these amplitudes is given by
A11'/A12'=tan .theta.start (3')
Therefore, the phase difference detection unit 42' calculates the
phase .theta.start of the reference signal S3 at the generation
time of the start signal M1, by
start=tan.sup.-1(A11'/A12') (4')
The phase difference detection unit 42' temporarily stores this
calculation result in a storage area not illustrated.
[0164] Further, the time difference measuring device 40' generates
the stop signal M2 illustrated in FIG. 8(a) at a detection timing
of the reflected laser beam L2 by the photo-detection element 21;
and the amplitude detection unit 45' samples/holds the reference
signal S3 at the generation timing t2 of the stop signal M2, and
detects the amplitude A21' of the reference signal S3 at the
generation timing t2.
[0165] Further, the amplitude detection unit 45' applies processing
to delay the stop signal M2 by the time .DELTA.t2 equivalent to the
phase .pi./2[rad] of the reference signal M3 from the generation
timing t2, generates a same pulse signal M2' as the stop signal M2
at the delay timing t2' (=t2+.DELTA.t2), samples/holds the
reference signal S3 by the pulse signal M2' generated at the delay
timing t2', and detects the amplitude A22' of the reference signal
S3 at the delay timing t2'.
[0166] Here, the amplitudes A21', A22' of the reference signal S3
acquired by sampling and holding can be expressed as follows, using
the phase .theta.stop from the generation time of the reference
signal S3.
A21'=A0 sin .theta.stop (5')
A22'=A0 sin(.theta.stop+.pi./2) (6')
Here, .theta.stop=2.pi.(t2/Ts), using the cycle Ts of the reference
signal S3.
[0167] Here, the formula (6') can be transformed into the
following:
A22'=A0 cos(.theta.stop (6'')
The formulas (5') and (6'') show that taking the amplitude A21' at
the generation timing t2 of the stop signal M2 on the vertical axis
and taking the amplitude A22' at the generation timing t2' of the
stop signal M2 on the horizontal axis will locate the intersection
of both the amplitudes A21', A22' on the circumference of a circle,
as illustrated in FIG. 8(c).
[0168] The ratio of these amplitudes A21'/A22' is given by
A21'/A22'=tan .theta.stop (7')
Therefore, the phase difference detection unit 42' calculates the
phase .theta.stop of the reference signal S3 at the generation time
of the stop signal M2, by
.theta.stop=tan.sup.-1(A21'/A22') (8')
The phase difference detection unit 42' temporarily stores this
calculation result in a storage area not illustrated.
[0169] Then, the phase difference detection unit 42' reads out the
two phases .theta.start, .theta.stop stored in the storage area,
and calculates the phase difference .DELTA..theta. of the reference
signal S3 corresponding to the time difference between the
generation time of the start signal M1 and the generation time of
the stop signal M2 by
.DELTA..theta.=.theta.stop-.theta.start (9)
[0170] When the generation time difference .DELTA.t of both the
pulse signals M1, M2 is shorter than the one cycle Ts of the
reference signal S3, the generation time difference .DELTA.t of
both the pulse signals M1, M2 can be calculated on the basis of the
above phase difference .DELTA..theta. and the cycle Ts, by
.DELTA.t=(.DELTA..theta./2n)Ts (10)
[0171] Here, the phase difference .DELTA..theta. that the phase
difference detection unit 42' calculates by the formula (9) takes a
value within 0[rad] to 2.pi.[rad]. Since the reference signal S3 is
a periodic signal, the calculated phase difference .DELTA..theta.
latently includes 2.pi.+.DELTA..theta., 4.pi.+.DELTA..theta., . . .
, in addition to 66 .theta..ltoreq.2.pi., and it can be expressed
as the general formula: 2.pi.(n-1)+.DELTA..theta. (n: natural
number).
[0172] On the other hand, as the generation time difference
.DELTA.t of both the pulse signals M1, M2 to be calculated, the
phase difference 2.pi.(n-1)[rad] being the first term of the above
general formula needs to be converted as well, and the natural
number n is required to be specified.
[0173] Accordingly, even if the generation time difference .DELTA.t
of both the pulse signals M1, M2 exceeds a time equivalent to one
cycle (2.pi.[rad]) of the reference signal S3, the coarse time
difference detection unit 43 detects the time difference .DELTA.t
in brief with the resolution of about one cycle of the reference
signal S3.
[0174] Then, referring to the coarse time difference ta detected by
the coarse time difference detection unit 43, the time difference
calculation unit 44 selects the time difference .DELTA.t most
approximate to the coarse time difference ta as the time difference
to be determined, among the time differences .DELTA.t
(=(.DELTA..theta./2.pi.)Ts) by the formula (10) corresponding to
the phase differences .DELTA..theta. (={.DELTA..theta.,
2.pi.+.DELTA..theta., 4.pi.+.DELTA..theta., . . . ,
2.pi.(n-1)+.DELTA..theta., . . . }) detected by the phase
difference detection unit 42'.
[0175] According to the above arithmetic operation, the time
difference measuring device 40' of the surveying device 100' in
this embodiment calculates the generation time difference .DELTA.t
of the start signal M1 and the stop signal M2.
[0176] Then, the distance conversion unit 31 of the distance
measuring means 30' calculates a distance D to the distance
measuring object 90 on the basis of the time difference .DELTA.t
measured by the time difference measuring device 40', by the
following formula (11). Here, the constant c in the formula (11)
represents the speed of light [m/sec].
D=c.DELTA.t/2 (11)
[0177] The distance D to the distance measuring object 90 thus
measured is outputted by the distance measurement result output
unit 50, so that a user of the surveying device 100' can grasp the
distance D.
[0178] Here, the distance measurement result output unit 50 is a
display device or the like that displays the measured distance D to
the distance measuring object 90 as numeric information, however it
may display various setting information on the surveying device
100' and so forth, in addition to the distance D.
[0179] According to the time difference measuring device 40' and
surveying device 100' in this embodiment, only one-time detection
of the amplitude of the reference signal S3 at each of the
generation timings of a pair of the start signal M1 and the stop
signal M2 and the delay timings thereof will accurately determine
the generation time difference between both the signals M1, M2,
thus leading to quickening the measurement of a time difference and
distance.
[0180] By applying a sine wave signal (or cosine wave signal) to
the reference signal S3, and applying the phase difference
.pi./2[rad] (this phase difference may be the odd-number times of
.pi./2[rad]) in the reference signal S3 to the delay times
.DELTA.t1, .DELTA.t2 of the pulse signals M1, M2, calculating
directly detected values (amplitudes) and calculating arc tangents
of ratios of the amplitudes will produce the phases .theta.
(.theta.start, .theta.stop) corresponding to the reference signal
S3 at the generation timing of the pulse signals M1, M2 and the two
phases thus obtained will give a phase difference
.DELTA..theta..
[0181] The variations in time of the phase calculated by the arc
tangent always become constant; therefore, regardless of the
generation timings of the two pulse signals to the reference
signal, a constant resolution and detection sensitivity can be
acquired.
[0182] Here, the construction illustrated in FIG. 3 can be applied
to the measuring light emission means 10 and the reflected light
detection means 20, in the same manner as the embodiment 1.
[0183] Further, as an example, the construction illustrated in FIG.
9 can be applied to a concrete control system of the time
difference measuring device 40'.
[0184] In the control system illustrated, an oscillator (TXCO) 41a'
outputs a pulse signal of 15 MHz, based on which a sine wave
generator (Sin) 41b' generates a sine wave reference signal S3. The
sine wave reference signal S3 passes a bandwidth limitation by a
band-pass filter (BPF) 42b'. The photo-detection element (APD) 21
detects the laser beam L1 and the reflected laser beam L2, based on
which a pulse detector (Puls Det) 42a' generates the start signal
M1 and the stop signal M2. At the generation timings of the start
signal M1 and the stop signal M2 and at the delay timings of the
start signal M1 and the stop signal M2 of which phases are delayed
by .pi./2[rad] by the delay circuit 42d', an A/D converter (A/D)
42c' samples/holds the reference signal S3 subjected to the
bandwidth limitation. The sampled/held values, that is, the
amplitudes A11', A12', A21', and A22' are inputted to the CPU
44a.
[0185] On the other hand, the output pulse from the oscillator 41a'
is inputted to the pulse counter (CNTR) 43a. The pulse counter 43a
counts the pulse number of the output pulse inputted between the
two generation timings of the start signal M1 and the stop signal
M2 generated by a pulse detector 42a'. The counted result is
inputted to the CPU 44a, which is provided for the calculation of
the coarse time difference ta by the CPU 44a. The memory (RAM) 44b
connected to the CPU 44a stores calculation results and various
constants.
[0186] The time difference measuring device and the distance
measuring device according to the invention is one that only
one-time detection of the reference signal S3 at each of the
generation timings t1, t2 and delay timings t1', t2' of the two
pulse signals generated with a time difference (four times in
total) accurately determines the time difference between these two
pulse signals; however, in a practical measurement, it is
preferable to measure plural times, to calculate the averages and
standard deviations, etc. of the plural measurement results, and to
enhance the reliability of measurement.
[0187] Now, the control system illustrated in FIG. 9 is constructed
to output the start signal M1 plural times so that the output pulse
from the oscillator 41a' being a source of generating the reference
signal S3 synchronizes with the start signal M1 at each
predetermined cycle of the output pulse (the phase difference
thereof becomes zero).
[0188] Since the reference signal S3 is synchronous with the output
pulse from the oscillator 41a', the reference signal S3 and the
start signal M1 are synchronized at each predetermined cycle of the
reference signal S3 by this control system.
[0189] Here in this control system, the 99.sup.th cycle of the
reference signal S3 and the 100.sup.th cycle of the start signal M1
are set to become synchronous.
[0190] That is, a first frequency divider (Divider) 11a applies
1/99 frequency dividing to the output pulse outputted from the
oscillator 41a', and the frequency of the output pulse becomes
151.51 kHz. This frequency is multiplied by 100 by a synthesizer
(SYH) 11b to become 15.151 MHz, thus the 100.sup.th cycle becomes
synchronous with the 99.sup.th cycle of the output pulse of 15 MHz
in the phase difference zero.
[0191] Further, a second frequency divider (Div) 11c applies
1/(23.times.77) frequency dividing to the signal of 15.151 MHz
being the result of multiplication by the synthesizer 11b. This
frequency-divided output pulse is inputted to a driver (DRIVER)
11d, and the driver 11d drives the PLD 11 to output the pulse laser
beam L1.
[0192] Thus, the PLD 11 repeatedly emits the pulse laser beam L1
with the frequency of about 8.5 kHz. Along with the repeated
emissions of the laser beam L1, the reflected laser beam L2 is
repeatedly detected, which makes it possible to measure multiple
times the time difference between the start signal M1 and the stop
signal M2. Thus, the reliability of measurement can be enhanced
through measurements by multiple times.
[0193] In the control system illustrated in FIG. 9, the reference
signal S3 and the start signal M1 are made up to be synchronous;
however, these signals are not necessarily to be synchronous. Both
the signal S3, M1 may be not completely synchronous, that is,
completely asynchronous, which depend on only the signals outputted
individually from mutually independent two oscillators, and do not
depend mutually, as illustrated in FIG. 10, for example.
[0194] In the control system illustrated in FIG. 10, the control
system that generates the reference signal S3 is completely
independent from the control system that emits the laser beam L1
from the PLD 11. The control system that generates the reference
signal S3 is the same as the control system illustrated in FIG. 9.
On the other hand, the control system that emits the laser beam L1
from the PLD 11 depends on an output pulse from the oscillator
(OSC) 11e being completely independent from the oscillator 41a'.
The frequency divider (Div) 11f applies frequency dividing to the
output pulse outputted from the oscillator 11e; based on the
frequency-divided output pulse, the driver (DRIVER) 11g drives the
PLD 11. Thus, the laser beam L1 is emitted from the PLD 11 at a
totally independent timing from the generation timing of the
reference signal S3.
[0195] The time difference measuring device and the distance
measuring device having the control system thus constructed are
able to enhance the reliability of measurement by measuring plural
times.
[0196] This embodiment applies a semiconductor laser to the light
source of the surveying device in the above description; however,
the surveying device according to the invention is not restricted
to the mode of the light source. A light source that emits the
other type of laser beam, a light source that emits light other
than a laser beam, and a measuring wave emission source that
generates a measuring wave such as a microwave other than light,
etc. can be applied. When any of these is applied, the case
exhibits the same function and effect as this embodiment.
[0197] Now, based on the amplitudes A11', A12' being the actually
detected values can be calculated the phase .theta.start, and based
on the amplitudes A21', A22' can be calculated the phase
.theta.stop. In the embodiment 1, since the reference signals S1,
S2 are generated each separately, there can be a case wherein the
maximum amplitudes A0 of both the reference signals S1, S2 are not
completely identical, or both the reference signals S1, S2 are not
completely synchronous when generated.
[0198] However, since the reference signal S3 is single in this
embodiment, different from the embodiment 1, it is not necessary to
consider the synchronization or identity between plural reference
signals as the embodiment 1.
[0199] The embodiments have been described as illustrative
examples; however this invention is not restricted to these. A
person having ordinary skill in the art will understand that
various improvements and modifications to the construction of this
invention are possible without departing from the scope and spirit
of the invention. From the view point of the above description,
this invention intends to include the improvements and
modifications thereof, and such improvements and modifications will
be included within the scope of the claims and the equivalents.
[0200] The present application claims the priority on the basis of
the Japanese Patent Application No. 2004-291495 filed on Oct. 4,
2004 and the Japanese Patent Application No. 2005-169500 filed on
Jun. 9, 2005, and incorporates herein all the contents including
the descriptions, drawings, and claims of those applications by
reference.
INDUSTRIAL APPLICABILITY
[0201] The above embodiments described the surveying device as an
example of the distance measuring device including the time
difference measuring device of the present invention; however the
invention is not restricted to this, and it is applicable to a
technical field that measures a time difference between pulse
signals with an extremely short time interval, or a technical field
that demands a quick and high-precision distance measurement, such
as a distance measuring device intending to include a natural
object likely to be displaced by environmental influences such as a
wind in a distance measuring object, and a figure measuring device
that specifies the outline figure of a distance measuring object by
measuring the distance to the distance measuring object and so
forth.
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